Are You Confident of the Diagnosis?

What you should be alert for in the history

Characteristic findings on physical examination

Diabetic dermopathy presents as brown or pink well-demarcated macules or flat-topped papules on the bilateral pretibial areas of patients with diabetes mellitus. Typically, the lesions are round or oval and are less than 1cm in diameter, but larger patches are occasionally seen. They may be smooth or mildly scaly. The surface is sometimes slightly depressed with a sharp drop-off from normal adjacent skin. The arrangement of lesions is often grouped and occasionally linear. No pain or pruritus is associated.

New lesions have been observed to arise as pink macules and then fade to a brown color. Resolution of individual lesions sometimes occurs slowly over time, while other lesions persist and accumulate on the pretibial areas. Rarely, diabetic dermopathy involves the thighs, upper extremities, or trunk (Figure 1).

Figure 1.

Diabetic dermopathy. Brown macules on the shin. Fine, diffuse scaling of asteatotic dermatitis is evident as an incidental unrelated finding.

Expected results of diagnostic studies

Diagnosis is typically established by the clinical features. Only uncommonly is skin biopsy considered to rule out other disorders. Histopathologically the epidermis may appear unremarkable or may demonstrate effacement of the rete ridges. In the papillary dermis, telangiectatic vessels are surrounded by a scant inflammatory infiltrate of lymphocytes and plasma cells with extravasated erythrocytes and/or deposits of hemosiderin. Diabetes-associated changes are evident within small vessels of the dermis and subcutis, both within the lesions of diabetic dermopathy and within non-lesional skin from diabetic patients. In diabetes, the small dermal and subcutaneous vessels have thickened walls that contain PAS-positive material.

The clinical differential diagnosis includes pigmented purpuric dermatitis, stasis dermatitis, and early lesions of necrobiosis lipoidica. All of the above conditions show a predilection for the lower extremities. Diabetes mellitus is usually considered a prerequisite for the diagnosis of diabetic dermopathy.

Compared with pigmented purpuric dermatitis, diabetic dermopathy is more strictly localized to the pretibial areas in the great majority of cases. Pigmented purpuric dermatitis may localize to the lower legs but is often more widespread and may include involvement of the thighs, trunk, or arms. In addition, the various types of pigmented purpuric dermatitis may demonstrate distinctive clinical features, such as the orange-brown color and cayenne pepper dots of Schamberg's disease, the gold color of lichen aureus, or the annular configuration of purpura annularis telangiectodes of Majocchi.

Histologically, pigmented purpuric dermatitis often shows a more intense perivascular lymphocytic infiltrate. Some specific variants of pigmented purpuric dermatitis also have distinctive histopathologic features, such as a lichenoid inflammatory infiltrate, which would not be seen in diabetic dermopathy.

Diabetic dermopathy must also be distinguished from stasis dermatitis. Stasis dermatitis has a predilection for the medial malleolus and medial leg and typically presents as broad red, purple, or brown patches, associated with pedal edema and venous insufficiency. Ulcerations or erosions may also be present. By contrast, the lesions of diabetic dermopathy are smaller brown or pink macules and are localized mostly on the pretibial areas. The lesions of diabetic dermopathy appear to be less inflamed, and are not associated with ulceration. Stasis dermatitis may be pruritic or tender, while diabetic dermopathy is asymptomatic.

Histopathologically, stasis dermatitis demonstrates heavier deposition of hemosiderin, more dermal inflammation and fibrosis, and more epidermal spongiosis than would be seen in diabetic dermopathy.

Necrobiosis lipoidica and diabetic dermopathy share an association with diabetes mellitus and a predilection for the pretibial area. The two entities may co-exist in the same patient. The earliest lesions of necrobiosis lipoidica may clinically resemble diabetic dermopathy, but the distinction becomes evident with time. Fully developed plaques of necrobiosis lipoidica are broader, more firm, and more inflamed than the macules of diabetic dermopathy. In addition, necrobiosis lipoidica often shows an annular morphology, with a central atrophic yellow or pink zone, and a peripheral red or brown zone. The lesions of diabetic dermopathy are smaller, more uniform macules.

Histopathologically, necrobiosis lipoidica demonstrates granulomatous dermal inflammation and zones of necrobiotic collagen. These microscopic findings are not seen in diabetic dermopathy. However, skin biopsy would only rarely be needed to distinguish the two entities, since the clinical features are typically distinctive in fully developed lesions.

Who is at Risk for Developing this Disease?

Diabetic dermopathy is the most common dermatologic manifestation of diabetes mellitus and is associated with both insulin dependent and non-insulin dependent diabetes. Among diabetic patients, the estimated incidence of diabetic dermopathy ranges from 9% to 55%. Diabetic dermopathy is especially frequent in patients over 50 years of age with longstanding diabetes mellitus.

What is the Cause of the Disease?

Etiology

Pathophysiology

The pathogenesis of diabetic dermopathy is unknown. A leading theory suggests a microangiopathy due to diabetes mellitus.

Systemic Implications and Complications

The importance of diabetic dermopathy lies in its systemic implications. Most patients with diabetic dermopathy are already known to have longstanding diabetes mellitus. In the absence of a known history of diabetes, lesions clinically resembling diabetic dermopathy should prompt an evaluation for undiagnosed diabetes mellitus. The following test results, obtained on 2 occasions, are diagnostic of diabetes mellitus: fasting plasma glucose greater than or equal to 126mg/dL or hemoglobin A1C greater than or equal to 6.5%.

In patients already known to have diabetes mellitus, the diagnosis of diabetic dermopathy is important because of its association with diabetic microangiopathic complications including retinopathy, neuropathy, and nephropathy.

Treatment Options

No effective treatment is known. Therapeutic measures are not recommended. In diabetic patients, it may be particularly advisable to avoid destructive modalities for diabetic dermopathy, due to the risk of infection, impaired wound healing, and chronic ulcers.

Glycemic control has not been demonstrated to have an effect upon the natural history of diabetic dermopathy. Nevertheless, conscientious management of glucose levels is important in patients with diabetic dermopathy, in view of the association with microangiopathic complications of diabetes mellitus.

Optimal Therapeutic Approach for this Disease

Glycemic control is recommended for the prevention of diabetic complications, although there may be no effect upon the diabetic dermopathy. No other treatment options are specifically recommended.

Patient Management

When diabetic dermopathy is identified, the patient should also be examined for other cutaneous manifestations of diabetes mellitus. Specifically, examination of the feet may be helpful to screen the patient for dermatophyte infection, interdigital erythrasma, or incipient foot ulcers.

Unusual Clinical Scenarios to Consider in Patient Management

Occasionally, non-diabetic patients may present with lesions clinically resembling diabetic dermopathy, but have no current or past evidence of diabetes mellitus. It is unclear whether the typical lesions of diabetic dermopathy ever occur in non-diabetic patients. In this clinical situation, a punch biopsy may be reasonable to rule out other diagnostic considerations.

(Turkish study of 166 diabetic men with peripheral neuropathy, diabetic dermopathy, or diabetic foot ulcers. Similar to the study described above for female patients, this study in diabetic men suggests an association between diabetic dermopathy and more severe neuropathy.)

(Italian study of 457 consecutive diabetic patients at an outpatient clinic. Diabetic dermopathy was identified in 12.5% of subjects and was the most frequent non-infectious cutaneous manifestation of diabetes in this group of patients.)

(Israeli study of 173 patients with diabetes mellitus. Diabetic dermopathy was present in 40% of patients and was more common in patients 50 years of age and older. Diabetic dermopathy was demonstrated to have a statistically significant association with retinopathy, nephropathy, and neuropathy.

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